Gall wasp infestations of eucalyptus trees have occurred in both the Northern and Southern hemispheres and pose a threat to commercial eucalyptus farming in China, Australia, Israel and Brazil. Efforts to control gall wasp infection of eucalyptus have included attempts to isolate naturally resistant plants and natural predators. These efforts have met with limited or no success. The protective environment of the gall in which gall wasps develop makes chemical pesticide control of gall wasps difficult.
Even when feasible, chemical pesticide control has disadvantages. Chemical pesticides are potentially detrimental to the environment, are not selective and are potentially harmful to non-target crops and fauna. Chemical pesticides persist in the environment and generally are metabolized slowly, or not at all. Chemical pesticides accumulate in the food chain, particularly in the higher predator species where they can act as mutagens and/or carcinogens to cause irreversible and deleterious genetic modifications. Crop pests, moreover, may develop resistance against chemical insecticides because of repetitive usage of the same insecticide or of insecticides having the same mode of action.
RNA interference or “RNAi” is a process of sequence-specific down-regulation of gene expression (also referred to as “gene silencing” or “RNA-mediated gene silencing”) initiated by double-stranded RNA (dsRNA) that is complementary in sequence to a region of the target gene to be down-regulated. Down-regulation of target genes in multicellular organisms by means of RNA interference (RNAi) has become a well-established technique. U.S. patent application publications US 2009/0285784 A1 and US 2009/0298787 relate to dsRNA as an insect control agent and are hereby incorporated herein by reference in their respective entireties. U.S. Pat. No. 6,506,559, U.S. patent application publication 2003/00150017 A1, International Publications WO 00/01846, WO 01/37654, WO 2005/019408, WO 2005/049841, WO 05/047300 relate to the use of RNAi to protect plants against insects. Each of the foregoing patents and published applications is hereby incorporated by reference in its entirety.